I. Definitions
As used herein, the phrase “group III-V” refers to a compound semiconductor that includes a group V element and at least one group III element. Moreover, the phrase “III-Nitride” refers to a compound semiconductor that includes nitrogen (N) and at least one group III element, including aluminum (Al), gallium (Ga), indium (In), and boron (B), and including but not limited to any of its alloys, such as aluminum gallium nitride (AlxGa(1-x)N), indium gallium nitride (InyGa(1-y)N), aluminum indium gallium nitride (AlxInyGa(1-x-y)N), gallium arsenide phosphide nitride (GaAsaPbN(1-a-b), and aluminum indium gallium arsenide phosphide nitride (AlxInyGa1-x-y)AsaPbN(1-a-b)), for example. III-Nitride also refers generally to any polarity including but not limited to Ga-polar, N-polar, semi-polar or non-polar crystal orientations. A III-Nitride material may also include either the Wurtzitic, Zincblende, or mixed polytypes, and may include single-crystal, monocrystalline, polycrystalline, or amorphous structures.
Also as used herein, the phrase “group IV” refers to a semiconductor that includes at least one group IV element, including silicon (Si), germanium (Ge), and carbon (C), and also includes compound semiconductors such as SiGe and SiC, for example. Group IV may also refer to a semiconductor material which consists of layers of group IV elements or doping of group IV elements to produce strained silicon or other strained group IV material. In addition, group IV based composite substrates may include semiconductor on insulator (SOI), separation by implantation of oxygen (SIMOX) process substrates, and silicon on sapphire (SOS), for example.
II. Background Art
Power transistors, such as group III-V field-effect transistors (group III-V FETs) and group III-V high electron mobility transistors (group III-V HEMTs) are often utilized in high power switching applications. For example, III-Nitride HEMTs may be utilized to provide switching and/or amplification functions.
As the voltage requirements for power transistors continue to increase, ever longer gates are required to provide punch-through resistance when the power transistor is in the blocking state, i.e., turned off. However, longer gate lengths may be associated with degradation of the conduction channel underlying the gate due to damage to the power transistor surface during fabrication.